1. Field of the Invention
The present invention relates to an information processing system having reduced direct intervention of a CPU to a magnetic disc unit.
2. Description of the Prior Art
In an information processing system which transfers data to and from a magnetic disc unit, efficiency of data transfer largely depends on the performance of a processor in the information processing system. A sector format is determined largely depending on the performance of the processor and a split sector format, a sequential sector format or the like may be selected. In the split sector format, sector addresses to a sequence of physical sectors on one track are assigned at an interval of one or more. In order access to all areas of the track, two revolutions of the disc are required for the split sector format having an interval of one and more revolutions are required for the split sector format having the interval of more than one. This is explained below in further detail.
FIG. 1 shows a block diagram of prior art system, in which numeral 1 denotes a central processing unit (CPU), numerals 2a and 2b denote latches, numeral 3 denotes a disc storage unit, numeral 4 denotes a buffer, and numeral 5 denotes an error check circuit.
FIG. 2 shows a data format (split sector format) to be processed by the system shown in FIG. 1. When a sector (SC) #6 designated by A in FIG. 2 is to be processed the CPU 1 instructs the disc storage 3 to read the sector #6 and write the content of the sector #6 in the buffer 4. Then, in time periods T=3 and T=4, the CUP 1 checks any error in the content of the sector #6 with the error check circuit 5 based on a signal from the latch 2b. The CPU 1 then determines if the next sector is to be processed or not. This process is called a sector interleave. In the illustrated example, the sector interleave process requires three revolutions of the disc to process all of the sectors on one track and hence a long process time is required.
In the sequential sector format, the sector addresses are assigned in the sequence of physical sectors on one track. In order to process the sectors in sequence, a high speed processor and complex control are required. As a result, hardware volume increases.
In a data storage such as a magnetic disc unit, a sector format usually comprises, as shown in FIG. 3, a gap 1 (G1) which is a synchronizing area for processing an ID field and starts at a sector pulse (SP), an identification field (ID) which stores address data and an attribute of a data field, a gap 2 (G2) which is a blank area between the ID field and the data field and used to synchronize the data field, the data field (DATA) which stores real data, and a gap 3 (G3) which is a dummy area at the end of the sector. In a conventional control system, the gap 3 is used to identify a boundary between the sectors and to allow a higher order unit to set a status. Thus, one sector comprises the gaps G1, G2, and G3 and the ID field and the data field. The data field is accessed to read or write the data (real data) to be processed. In order to assure correct access to a specified sector on a specified track, the ID field is read and compared.
In the sequential sector format, a checking process and a software process have to be carried out in a short time during the gaps G1, G2 and G3. Consequently, complex and fast control is required and hence hardware volume increases and an expensive control circuit is required.